Finned tube produced from continuous strip



United States Patent U.S. Cl. 165184 2 Claims ABSTRACT OF THE DISCLOSURE The finned tube formed from continuous strip comprises a tubular portion having two or more flat sides and integral separate flat fins extending outwardly from each flat side, said fins having uniform thickness equal to the original thickness of the strip.

It is an object of the present invention to provide a finned tube having a transverse elongated shape comprising generally semi-circular edges interconnected by fiat or planar side walls, the fins at the flat sides of the tube being of relatively great width as compared to the width of the fins at the rounded edges thereof.

It is a further object of the present invention to produce a tube of the character described in the preceding paragraph in which the strip material is slit so as to provide relatively large fin-forming areas in the zones opposite the flat side portions of the tube.

Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings, illustrating preferred embodiment of the invention, where- FIGURE 1 is a fragmentary view of strip material cut to prepare it for subsequent tube forming operations.

FIGURE 2 is an end view showing the strip material of FIGURE 1 bent into generally U-shaped cr0ss-sectional configuration.

FIGURE 3 is a fragmentary elevational view showing the elongated folded strip material of FIGURE 2 coiled into a closed generally helical configuration to form a finned tube.

FIGURE 4 is a fragmentary section on the line 4-4, FIGURE 3.

FIGURE 5 is a view similar to FIGURE 1 illustrating a different pattern of cuts to produce fins having a double thickness of material.

FIGURE 6 is a view of the strip material shown in FIGURE 5 bent into U-shaped cross-sectional configuration.

FIGURE 7 is a sectional view similar to FIGURE 4 showing a different cross-sectional configuration of tube and mandrel.

Referring first to FIGURES 1-4, elongated strip material 10 preferably of metal is transversely cut to provide slits 11 extending from one edge 12 to a point adjacent to but spaced somewhat from the opposite edge 13. At the inner edge of the slits 11 the strip material is provided with short cuts to provide through slots 14. If desired, the strip material may also be scored along the dotted lines 16 and 18 for subsequent bending although the bending may be accomplished without scoring the strip.

Referring now to FIGURE 2 the strip of FIGURE 1 is bent along the lines 16 and 18 into the generally U-shaped configuration shown. The material intermediate the dotted line 18 and the edge 13 forms the narrow continuous upstanding flange 20, the material intermediate the dotted line 16 and the slots 14 forms similar narrow "ice longitudinally spaced flange portions 22, and the material intermediate adjacent slits 11 forms a series of upstanding flange portions 23 which in the folded strip have adjacent edge portions.

The next step in the production of the integral finned tube is to wind the generally U-shaped strip shown in FIGURE 2 around a mandrel a portion of which is shown at 24. The mandrel 24 has the transversely elongated cross-sectional shape illustrated in FIGURE 4 which it will be observed comprises generally semi-cylindrical edge portions 26 interconnected by flat side portions 28. The U-shaped strip of FIGURE 2 is wound tightly so that the narrow continuous flange portion 20 is in abutment with the longitudinally spaced narrow flange portions 22 and with the inner portion of the fin-forming portions 23. Since the flanges 20 and 22 are relatively narrow the U-shaped strip material may be wound tightly around the mandrel without additional treatment. It 'will be understood that as the strip material is wound around the semicylindrical end portions of the mandrel the radially outer edge portions of the narrow flanges 20 and 22 are required to be elongated relative to the base portion of the flanges. However, by keeping the flanges 20 and 22 sufficiently narrow this stretching takes place without diificulty. As an alternative, the narrow flange portions 20 and 22 may be rolled longitudinally to provide an outward taper.

The spacing of the slits 11 and slots 14 is such that the material of the strip intermediate the ends of adjacent slots lies at the flat side of the mandrel and hence at the flat side of the tube when the material is wound into a tight configuration. The entire fin-forming portion including corner portions 26 remains in flat condition while generally U-shaped strip shown in FIGURE 2 is coiled into the tubular configuration illustrated in FIGURE 4.

The construction is completed by providing a suitable bond between the continuous narrow flange 20 and the short narrow flange portions 22 and the inner portions of the flat fin-forming portions 23. This bonding is accomplished by welding, soldering, brazing, or the like depending upon the nature of the material from which the tube is formed.

By employing the spaced relatively large fin-forming areas in conjunction with the relative narrow flanges for bonding together and sealing adjacent convolutions of the tube, the effective heat transfer area dependent on the fin area may be substantially as large as desired, while the flange portions employed in bonding adjacent convolutions together may be sufliciently narrow so that the U-shaped strip material may be bent into the required cross-sectional configuration without special treatment of the narrow flange portions.

Referring now to FIGURE 5 there is illustrated a somewhat different embodiment in which the strip 30 is relatively wider and is provided with cuts forming slits 31 extending into the strip from opposite side edge portions. Each of the slits 31 extends into One of a series of longitudinally spaced slots 33. The strip material if desired may be scored along bend lines indicated at 34 and 35. In any case, the strip is next bent into the U-shaped configuration shown in FIGURE 6 in which the material intermediate the bent lines 34 and 35 and the slots 33 produce short upstanding flange portions 36 and 38 on both sides of the U-shaped strip. As before, these short flange portions are bent around the generally semicylindrical edge portions of the mandrel 24. Since the relatively large fin-forming areas 40 are provided at bolh sides of the U-shaped strip of FIGURE 6, it 'will be understood that in the completed finned tube each finforming area 40 is positioned flat against an adjacent finforming portion 40, or in other words, the relatively large areas of the tube are of double thickness.

The generally oval or transversely elongated tube configuration is well suited to certain air-cooling applications Where minimum pressure drop is desired. This is due to the fact that the thin transversely elongated tube presents a better aerodynamic shape than several round tubes of equivalent surface area.

Referring now to FIGURE 7 there is illustrated another embodiment of the present invention in which the slotted tube, folded into generally U-shaped or channel configuration, is wound around a mandrel 42 of generally triangular shape having fiat sides 44 interconnected by rounded corners 46. In this case the bottom walls of the channel configuration define a continuous sealed tube 48 of generally triangular configuration and relatively large flat fins 50 extend outwardly from the tube 48 and specifically, from the flat sides 52 thereof formed by the flat sides 44 of the mandrel 42.

The drawings and the foregoing specification constitute a description of the improved finned tube and the method of producing the same in full, clear, concise and exact terms as to enable any person skilled in the art to practice the invention, the scope of Which is indicated by the appended claims.

What I claim as my invention is:

1. A unitary finned tube formed in its entirety of continuous bendable sheet metal of uniform thickness, comprising a tube portion formed of generally helically wound abutted and bonded convolutions, each convolution being of generally U-shaped cross-section with the bottom of the U-shape constituting the tube wall and the legs of the U being abutted and bonded together, said tubular portion having longitudinally extending fiat sides,

and enlarged flat fin areas each integral along one edge with an adjacent leg of the U-shape throughout substantially the entire width of a flat side thereof, and extending outwardly of the tube therefrom.

2. A tube as defined in claim 1 in which each leg of the U-shape of the tube has an edge connected fin portion, the fin portions of adjacent convolutions abutting in surface to surface contact to form fin areas of a thickness double the Wall thickness of the tube.

References Cited UNITED STATES PATENTS 2,480,706 8/1949 Brinen 165-179 X 2,537,797 1/1951 Simpelaar 165-179 3,202,212 8/1965 Kritzer 165179 3,222,764 12/1965 Hansson et 211. 165-181 X 1,294,465 2/1919 Horvath 138154 1,744,074 1/1930 Gortner 165-184 2,372,795 4/1945 Rodeck 165184 X 2,930,405 3/1960 Welsh 13838 FOREIGN PATENTS 420,347 11/1934 Great Britain. 316,887 12/1956 Switzerland.

LAVERNE D. GEIGER, Primary Examiner EDWARD J. EARLS, Assistant Examiner U.S. Cl. X.R. 138154 

